Lawn mower powered by cylinder deactivation engine

ABSTRACT

The lawn mower ( 10 ) comprises an internal combustion engine ( 100 ) having a plurality of cylinders, an engine control unit ( 110 ) for selectively deactivating at least one of the cylinders, a cutting blade ( 70 ) supported by a lawn mower main body via a cutter deck, and connected to the engine in a power transmitting relationship, a clutch ( 80 ) provided in a power transmission path between the engine and the cutting blade, a height adjustment mechanism ( 90 ) provided on the cutter deck for adjusting the height of the cutting blade, and a central control unit ( 50 ) for controlling an operation of the height adjusting mechanism, the clutch and the engine control unit. The central control unit is configured to cause the engine control unit to deactivate at least one of the cylinders when a prescribed operating condition is met, and to raise the cutting blade to a prescribed elevated height before deactivating the at least one of the cylinders.

TECHNICAL FIELD

The present invention relates to a lawn mower provided with a multiplecylinder internal engine configured to selectively deactivate at leastone of a plurality of cylinders.

BACKGROUND ART

JP2009-273386A discloses power equipment in the form of a ride-on mowerwhich is provided with cutting blades housed in a cutter deck. Thecutter deck can be adjusted vertically by manually operating a leverwhich is connected to the cutter deck via a linkage mechanism so thatgrass can be cut at a desired height. The cutting blades are rotated bythe power of the engine.

JP2007-315455A discloses a lawn mower provided with a cutting bladehoused in a blade housing. In this lawn mower, the blade is connected tothe output shaft of the engine via an electromagnetic clutch. When aclutch switch is turned on by the operator, the control unit of the lawnmower engages the clutch if an increase in the engine rotational speedis detected, and disengages the clutch if a decrease in the enginerotational speed is detected. This operation is cyclically repeated sothat the clutch can be finally engaged without stalling the engine.

JP2013-022987A discloses a ride-on mower provided with a cutting bladehoused in a blade housing. The mower is provided with driven wheelswhich are powered by an internal combustion engine via a hydrauliccontinuous transmission system. The control system of the mower detectsa steering operation of the mower, and reduces the speed of the drivenwheels when a steering action of the mower is detected.

In power equipment having a propelling device (such as wheels andcrawlers) and a work implement which are both powered by a same internalcombustion, it is desirable to appropriately allocate the power to thepropelling device and the work implement in such a way that the energyefficiency of the power equipment is optimized.

BRIEF SUMMARY OF THE INVENTION

In view of such problems of the prior art, and the recognition by theinventors, a primary object of the present invention is to provide powerequipment which can minimize fuel consumption.

To achieve such an object, the present invention provides a lawn mower,comprising: a lawn mower main body (15) provided with a propellingdevice; a power source (100) for selectively powering the propellingdevice; a traveling state sensor (40) for detecting a traveling state ofthe lawn mower; an internal combustion engine (100) having a pluralityof cylinders and supported by the lawn mower main body; an enginecontrol unit (110) for selectively deactivating at least one of thecylinders; a cutting blade (70) rotatably supported by the lawn mowermain body via a cutter deck (75) and connected to the engine in a powertransmitting relationship; a blade clutch (80) provided in a powertransmission path between the engine and the cutting blade; a heightadjustment mechanism (90) provided on the cutter deck for adjusting aheight of the cutting blade; and a central control unit (50) forcontrolling an operation of the blade clutch, the height adjustmentmechanism and the engine control unit; wherein the central control unitis configured to cause the engine control unit to deactivate at leastone of the cylinders when a prescribed operating condition is met, andto raise the cutting blade to a prescribed elevated height beforedeactivating the at least one of the cylinders.

Preferably, at least one of the cylinders of the engine may bedeactivated when the engine load is light so that the fuel economy ofthe lawn mower may be improved. However, it is possible that the cuttingblade may be operated at any time if the blade clutch is engaged, andthis may suddenly increase the engine load. The central control unitshould take such factors into account in determining the favorabletiming for deactivating at least one of the cylinders of the engine.

On the other hand, the central control unit may also positively increasethe likelihood of light engine load. For instance, the probability ofencountering a heavy engine load can be positively decreased by raisingthe height of the cutting blade.

Based on such a consideration, according to the present invention, thecentral control unit is configured to cause the engine control unit todeactivate at least one of the cylinders when a prescribed operatingcondition is met, and to raise the cutting blade to a prescribedelevated height before deactivating the at least one of the cylinders.The probability of encountering a heavy engine load can be positivelydecreased by raising the height of the cutting blade.

According to a certain aspect of the present invention, the centralcontrol unit is configured to deactivate at least one of the cylinderswhen the lawn mower is not traveling forward.

When the lawn mower is not traveling forward, it is highly likely thatthe engine load is light. Therefore, it is advantageous to deactivate atleast one of the cylinders when the lawn mower is not traveling forwardin order to save fuel without any detrimental effect.

According to another aspect of the present invention, the centralcontrol unit is configured to maintain the cutting blade at theprescribed elevated height when the lawn mower is commanded to travelrearward or is traveling rearward.

When the lawn mower is commanded to travel rearward or is travelingrearward, no grass cutting is typically intended. Therefore, it isadvantageous to maintain the cutting blade at the prescribed elevatedheight, and positively decrease the probability of a high engine load atsuch a time.

According to yet another aspect of the present invention, the lawn mowerfurther comprises a steering angle sensor, and the central control unitis configured to deactivate at least one of the cylinders when the lawnmower is traveling forward, and a steering angle greater than aprescribed value is detected.

When the steering angle is great, it is highly probable that the lawnmower is being displaced from one place to another or making a U turn atan end of a mowing pass, and the engine load is light. Therefore it isadvantageous to deactivate one of the cylinders to improve the fueleconomy of the lawn mower at such a time.

According to yet another aspect of the present invention, when the lawnmower is traveling forward, and a steering angle greater than theprescribed value is detected, the central control unit further raisesthe cutting blade to a prescribed elevated height and decelerates thelawn mower.

By decelerating the lawn mower when a steering angle greater than aprescribed value is detected, the precision in the turning maneuver ofthe lawn mower can be improved and/or the turning radius of the lawnmower can be minimized.

According to yet another aspect of the present invention, the prescribedelevated height corresponds to a highest possible position of the cutterdeck.

When the cutter deck is placed at the highest possible position, thelikelihood for the cutting blade to encounter a high load can beminimized.

Thus, the present invention provides a lawn mower which can minimizefuel consumption.

BRIEF DESCRIPTION OF THE DRAWING(S)

FIG. 1 is a functional block diagram of a ride-on lawn mower embodyingthe present invention;

FIG. 2 is a time chart showing a first mode of operation of the mower;

FIG. 3 is a flowchart showing the first mode of operation of the mower;

FIG. 4 is an additional part of the flowchart showing the first mode ofoperation of the mower;

FIG. 5 is a time chart showing a second mode of operation of the mower;

FIG. 6 is a flowchart showing the second mode of operation of the mower;

FIG. 7 is an additional part of the flowchart showing the second mode ofoperation of the mower;

FIG. 8 is a time chart showing a third mode of operation of the mower;

FIG. 9 is a flowchart showing the third mode of operation of the mower;and

FIG. 10 is an additional part of the flowchart showing the third mode ofoperation of the mower.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

A preferred embodiment of the present invention is described in thefollowing with reference to the appended drawings.

Referring to FIG. 1, a ride-on lawn mower 10 embodying the presentinvention is provided with an internal combustion engine 100 consistingof a multiple cylinder engine (two-cylinder engine in the illustratedembodiment) supported in a front part of a lawn mower main body 15. Acutting blade 70 that can be rotatively actuated by the engine 100 issupported by a central lower part of the lawn mower main body 15. In thecase of a lawn mower, as is the case with other forms of powerequipment, the engine 100 is required to power not only the propellingdevice consisting of driven wheels but also the work implementconsisting of a cutting blade 70; namely, in the illustrated embodiment,the engine 100 embodies both a power source for powering the propellingdevice and an internal combustion engine connected to the work implementin a power transmitting relationship. Therefore, in view of increasingthe operation efficiency, high output engines typically consisting ofmultiple cylinder engines are preferred in most situations.

In the illustrated embodiment, the engine 100 is provided with acylinder deactivation control device so that at least one of thecylinders may be selectively deactivated under a prescribed condition.The cylinder deactivation control device includes a central control unit50 consisting of an electronic control unit, and an engine control unit110 for controlling the operation of the engine 100. The engine controlunit 110 may be either separately provided from the central control unit50 or internally incorporated with the central control unit 50.

The central control unit 50 typically but not exclusively consists of amicrocomputer including a CPU, ROM and RAM. The ROM stores a computerprogram (cylinder deactivation control program) for instructing the CPUto execute a series of actions (cylinder deactivation control process),and the RAM provides a work area for the CPU. The ROM also storesvarious data that are required for the CPU to operate.

The engine control unit 110 is configured to adjust the rotational speedof the engine 100 which may be incorporated with a throttle by wiresystem, and may be configured to perform the functions of an enginegovernor. The rotational speed of the engine may be given by revolutionsper minute, “rpm”, but may also be given by an inverse of time (inminutes) required for each revolution, “min⁻¹”. The engine 100 isprovided with a sensor unit 120 that includes an rpm sensor fordetecting the rotational speed of the engine 100. The engine controlunit 110 receives a target rotational speed from the central controlunit 50, and controls the throttle valve 100 a of the engine 100 so thatthe engine speed detected by the rpm sensor coincides with the targetrotational speed.

The traveling speed of the lawn mower 10 can be controlled by thedepression stroke of an accelerator pedal (not shown in the drawings).The depression stroke may be detected by a detection unit 40 equipped inthe lawn mower 10. In the illustrated embodiment, the lawn mower 10 isequipped with a hydraulic transmission system which can be controlled bythe accelerator pedal. However, other forms of transmission systems mayalso be used in the present invention. At any event, the traveling speedof the lawn mower 10 can be controlled by the depression stroke of theaccelerator pedal under normal situations, but the central control unit50 is able to change the traveling speed of the lawn mower 10 withoutregard to the depression stroke of the accelerator pedal.

The detection unit 40 further includes a speed sensor (which may consistof a wheel speed sensor) for detecting the traveling speed of the lawnmower 10. The lawn mower 10 is fitted with an operation console 60 whichincludes a start switch for starting the engine and a blade switch forselectively connecting the cutting blade with the output shaft of theengine in a torque transmitting relationship.

The cutting blade 70 is connected to the output shaft of the engine 100via a blade clutch 80 consisting of an electromagnetic clutch.

The cutting blade 70 is rotatably supported by the blade deck 75 whichis in turn attached to the lawn mower main body 15 via a heightadjustment mechanism 90 including a linkage mechanism and an actuator(such as an electric motor). The blade deck 75 can be verticallyadjusted by actuating the electric motor of the height adjustmentmechanism 90 via the central control unit 50. This action may beperformed both automatically and manually as required.

FIG. 2 is a time chart showing a first mode of operation of the lawnmower 10. The operator starts the engine 100 at time ta1 by operatingthe start switch. The two cylinders are both in the activated conditionat this time, and the throttle valve is opened gradually from a fullyclosed state to Tha1 (F in FIG. 3).

The central control unit 50 monitors the rotational speed of the engine100, and monitors if the engine rotational speed is maintained at aprescribe speed Na1 in a stable manner (A in FIG. 2). Once the enginerotational speed has established a stable condition at speed Na1 at timeta2, the central control unit 50 deactivates one of the cylinders (C inFIG. 2) by controlling the engine control unit 110. At this time, inorder to compensate for the deactivation of one of the cylinders, thethrottle opening is increased to Tha2 (F in FIG. 2). At this time, theblade switch is still turned off (D in FIG. 2).

It is possible to start the engine with one of the cylindersdeactivated. However, if the engine is started with only one of thecylinders activated, it would take longer for the engine rotationalspeed to reach a stable condition.

It is also possible to deactivate one of the cylinders as soon as theengine is started. However, again, if the engine is warmed up with onlyone of the cylinders activated, it would take longer for the enginerotational speed to reach a stable condition, and may impair the fueleconomy of the engine owing to the prolonged period of instability inthe engine rotational speed.

Based on such considerations, once the engine rotational speed is placedin a stable condition at speed Na1, the central control unit 50deactivates one of the cylinders at time ta2 (C in FIG. 2). Thereby, thefuel economy of the engine can be improved. In other words, once therotational speed of the engine 100 is placed in a stable condition, evenwith one of the cylinders deactivated, the rotational speed of theengine 100 can be continued to be in a stable condition at speed Na1.

Furthermore, as the engine 100 is started with the two cylindersactivated at ta1, the time period required for the rotational speed ofthe engine 100 to reach a stable condition (the time interval betweenta1 and ta2) can be minimized.

As the throttle opening is increased from zero to Tha1 by the centralcontrol unit 50 via the engine control unit 110, the rotational speed ofthe engine 100 quickly increases from zero, and initially overshootsspeed Na1 to a significant extent (A in FIG. 2). The rotational speedthen oscillates around speed Na1 for a certain time period. The centralcontrol unit 50 determines that the engine rotational speed has reacheda stable condition once this oscillation has subsided to an acceptablelevel.

More specifically, the central control unit 50 determines if therotational speed of the engine 100 is held within a tolerable range ordetermines if the rotational speeds of the engine 100 sampled at aprescribed time interval have converged into a tolerable range. Thecentral control unit 50 determines that the rotational speed of theengine 100 is placed in a stable condition at time ta2, for instance,and starts the cylinder deactivation process at time ta2 (C in FIG. 2).This may be accomplished by defining a cylinder deactivation flag, andinitiating the cylinder deactivation process when the cylinderdeactivation flag is set to “1” instead of “0”. At this time, thethrottle opening is increased from Tha1 to Tha2 to maintain the samerotational speed Na1 with only one of the cylinders activated (F in FIG.2).

During the time interval in which one of the cylinders is deactivated,the central control unit 50 monitors if the rotation of the cuttingblade 70 is commanded. When the operator turns on the blade switch attime ta3, the central control unit 50 activates all of the cylinders (Cand D in FIG. 2). This may be accomplished by setting the cylinderdeactivation flag to “0” to terminate the cylinder deactivation processand activate all of the cylinders at time ta3.

Thus, the central control unit 50 keeps one of the cylinders deactivateduntil the operation of the cutting blade 70 is commanded, and activatesall of the cylinders once data or a signal indicating the need for theoperation of the cutting blade 70 is received from the operation console60. Therefore, the consumption of fuel is reduced during the time periodbetween time ta2 and time ta3.

In particular, when one of the cylinders is deactivated, the rotationalspeed of the engine is Na1. When the blade switch is turned on by theoperator at time ta3, the central control unit 50 activates all of thecylinders, and increases the rotational speed of the engine to Na2 atthe same time. Immediately following this, the central control unit 50engages the blade clutch 80 at ta4.

According to this arrangement, when the cutting blade 70 is required tobe operated, not only all of the cylinders are activated but also therotational speed of the engine 100 is increased so that the suddenincrease in the engine load caused by the engagement of the blade clutch80 is prevented from causing the stalling of the engine 100 or otherwiseplacing the engine in an unstable condition. Therefore, during theoperation of the mower 10, the possibility of stalling the engine 100can be reduced without regard to the operating condition of the mower10.

Once the blade clutch 80 is engaged, the central control unit 50maintains all of the cylinders activated, and maintains the rotationalspeed of the engine at the normal rotation speed of Na1. Thus, byreducing the rotational speed of the engine from the high level of Na2suitable for preventing the stalling of the engine to the normal levelof Na1 once the blade clutch 80 is engaged, the engine 100 is maderesistant against stalling while minimizing the fuel consumption.

The engine rotational speed sharply drops when the blade clutch 80 isengaged at time ta4 owing to the sudden increase in the engine load, butreturns to the normal rotational speed of Na1 in a short period of timeas the rotational speed of the cutting blade 70 stabilizes.

During the time interval between time ta2 and time ta3, the blade clutch80 is disengaged while the mower 10 is stationary or traveling.Therefore, the engine load is so light that the engine may be operatedwith only one of the cylinders in an adequately stable manner. As aresult, the fuel consumption can be minimized.

Preferably, when one of the cylinders is deactivated or during the timeinterval between time ta2 and time ta3, a highly lean mixture may besupplied to the combustion chamber of the active cylinder of the engineat a relatively wide throttle opening. In the illustrated embodiment,the throttle opening is increased from Th1 to Th2 at time ta2.

Thus, during the time interval between time ta2 and time ta3, the enginecan be operated in a stable manner in spite of a highly lean mixtureowing to the light load, and the increasing of the throttle openingreduces the pumping loss of the engine. As a result, the engine can beoperated in a highly fuel efficient manner.

Furthermore, during the time interval between time ta2 and time ta3 orwhen one of the cylinders is deactivated, the ignition timing of theengine may be advanced and/or the duration of the spark of the sparkplug may be increased so that a highly stable combustion may bemaintained.

When the deactivated cylinder is activated once again at time ta3, thecentral control unit 50 returns the air fuel ratio back to the normalvalue, and reduces the throttle opening back to Tha1. In other words,the lean burn control is maintained during the time interval betweentime ta2 and time ta3, and is turned off at time ta3.

FIGS. 3 and 4 show a flowchart of the mode of operation of the cylinderdeactivation control from the time of engine start up. When the engine100 is started, the central control unit 50 determines if the rotationalspeed of the engine 100 has stabilized at the rotational speed of Na1 instep ST01. If the rotational speed of the engine 100 has stabilized atthe rotational speed of Na1, the central control unit 50 monitors if theblade switch on the operation console 60 has been turned on in stepST02.

If the blade switch is turned off in step ST02, the central control unit50 determines if the cylinder deactivation process is to be startedaccording to the cylinder deactivation flag in step ST03. The cylinderdeactivation flag is initially set to “0”. If the cylinder deactivationflag is “0” in step ST03, the central control unit 50 determines if theload of the engine 100 is heavy in step ST04.

More specifically, if the throttle opening is constant or in a stablecondition, and additionally or alternatively, if the throttle opening isbelow a prescribed threshold value, the determination result of stepST04 is No. The sensor unit 120 is provided with a throttle sensor forthis purpose.

If the engine load is light in step ST04, the cylinder deactivation flagis set to or maintained at “1” in step ST05. Conversely if the engineload is heavy in step ST04, the cylinder deactivation flag is set to ormaintained at “0” in step ST06. Then, in either case, the program flowreturns to step STO1.

If the cylinder deactivation flag is “1” in step ST03, the centralcontrol unit 50 determines if the load of the engine 100 is heavy instep ST07. This determination step is similar to step ST04, and it isdetermined that the engine load is light if the throttle opening isconstant or in a stable condition, and additionally or alternatively, ifthe throttle opening is below a prescribed threshold value.

If the engine load is light in step ST07, the cylinder deactivation flagis maintained at “1”. Conversely if the engine load is heavy in stepST07, the cylinder deactivation flag is set to “0” in step ST08, and theprogram flow returns to step ST01.

If the rotational speed Ne of the engine 100 is not stable in step ST01,the cylinder deactivation flag is set to or maintained at “0” in stepST09, and the target rotational speed of the engine 100 is set to aprescribed rotational speed Na1 in step ST10. The target rotationalspeed of the engine 100 is initially (when the engine 100 is started)set to the prescribed rotational speed Na1. The blade clutch 80 is thendisengaged (OFF) or maintained in the disengaged state in step ST11, andthe program flow returns to step ST01. The blade clutch 80 is initially(when the engine is started) disengaged.

If the blade switch is turned on in step ST02, the central control unit50 determines if the blade clutch 80 is engaged in step ST12. If theblade clutch 80 is disengaged, step ST13 similar to step ST03 isexecuted to determine if the cylinder deactivation process is to bestarted.

If the cylinder deactivation flag is “1” in step ST13, the cylinderdeactivation flag is set to “0” in step ST14, and the target rotationalspeed of the engine 100 is set to Na2 which is higher than theprescribed rotational speed Na1 in step ST15. If the cylinderdeactivation flag is “0” in step ST13, the central control unit 50automatically engages the blade clutch 80 in step ST16. Step ST17similar to step ST15 is then executed to set the target rotational speedNe of the engine 100 to Na2. Following steps ST15 and ST17, the programflow returns to step ST01.

If the blade clutch 80 is engaged in step ST12, the central control unit50 determines if the rotational speed Ne of the engine 100 is maintainedat Ne2 in a stable manner in step ST18. If the rotational speed Ne ofthe engine 100 is maintained at Ne2 in a stable manner in step ST18, thecentral control unit 50 then sets the target rotational speed to theprescribed rotational speed Na1 in step ST19, and the program flowreturns to step ST01. If the rotational speed is not stable in stepST18, the program flow returns to step ST01.

FIG. 5 is a time chart showing the mode of operation of the lawn mower10 including the time point of starting a forward travel with the bladeclutch 80 already placed in the engaged state and the engine 100running. The throttle opening was initially Thb1, and the operatorincreases the throttle opening to Thb2 at time tb1 (E in FIG. 5). Thiscauses the lawn mower 10 to start traveling forward at time tb1 (F inFIG. 5).

The detection unit 40 detects the traveling speed of the lawn mower 10,and the central control unit 50 maintains the traveling speed of thelawn mower 10 at Vb1 which is greater than zero. At this time, becauseof the high loading placed on the engine 100, the two cylinders are keptactivated so that the rotational speed of the engine 100 may bemaintained at Nb2 in spite of the added loading required for propellingthe lawn mower 10.

If the cutting blade 70 does not cut grass while the lawn mower 10 istraveling forward, it is possible to deactivate one of the cylinders.However, as the blade clutch 80 is engaged, it is very possible that thecutting blade 70 starts cutting grass. Therefore, it is advantageous tokeep both of the two cylinders activated when the lawn mower 10 hasstarted traveling forward, and to continue to keep the two cylindersactivated until the operating condition of the engine 100 has stabilized(B in FIG. 5).

While the two cylinders are kept activated, following the time pointtb1, the central control unit 50 monitors if the throttle opening issmaller than a prescribed level Thb3. If a throttle opening smaller thanThb3 has persisted for more than a prescribed time period, the centralcontrol unit 50 deactivates one of the cylinders at time tb2 so that thefuel consumption may be saved (B and E in FIG. 5).

The fact that the throttle opening is smaller than Thb3 means that theloading of the engine 100 is light even though the cutting blade 70 isrotating. Therefore, the central control unit 50 can safely deactivateone of the cylinders at time tb2. Thus, at this time, the centralcontrol unit 50 sets the cylinder deactivation flag to “1” at time tb2to initiate the cylinder deactivation control, and the engine 100 isoperated with only one of the cylinders activated. At the same time, thethrottle opening is increased to Thb4 which is greater than Thb3 so thatthe rotational speed of Nb2 may be maintained with only one of thecylinders activated.

Following the time point tb2, the central control unit 50 continues tomonitor the throttle opening if the throttle opening is greater than aprescribed opening Thb5 which is higher than Thb4. If the throttleopening exceeds this threshold level Thb5, the central control unit 50causes the engine 100 to operate with both of the cylinders activated attb3 (B and E in FIG. 5). Thus, at this time, the central control unit 50sets the cylinder deactivation flag to “0” at time tb3 to interrupt thecylinder deactivation control, and the engine 100 is operated with bothof the cylinders activated.

Thus, when the engine loading is high (as detected by the throttleopening exceeding Thb5), both of the cylinders are activated so that theengine 100 is prevented from stalling or otherwise being placed in anunstable condition. In other words, both of the cylinders are activatedwhen the power requirement of the engine is high (such as when thecutting blade 70 is cutting grass while the lawn mower 10 is travelingforward) but until such a time, the engine is allowed to operate withonly one of the cylinders activated so that the fuel consumption can beminimized.

Alternatively, following the time point tb2, the central control unit 50monitors if the rotational speed of the engine 100 is maintained at Nb2in a stable manner. If the throttle opening exceeds Thb5 while therotational speed of the engine 100 is not stable at Nb2, the centralcontrol unit 50 interrupts the cylinder deactivation control, and causesboth of the cylinders to be activated at time tb3.

More specifically, the central control unit 50 determines if therotational speed of the engine 100 remains in a prescribed tolerancerange, or if the rotational speed of the engine 100 is within thetolerance range such as Nb2±ΔN at each sampling time Δt. If the centralcontrol unit 50 determines that the engine rotational speed is notstable at time tb3, the cylinder deactivation control is interrupted attime tb3.

Thus, the loading of the engine is determined from the fluctuations inthe engine rotational speed and the throttle opening in a highly exactmanner so that the cylinder deactivation control is interrupted onlywhen required. As a result, the cylinder deactivation control is keptturned on whenever possible, and the fuel consumption of the engine canbe minimized.

Following the time point tb3, the central control unit 50 determines ifthe lawn mower 10 is still traveling forward. When a zero speed of thelawn mower 10 is detected by the detection unit 40 at time tb4, thecentral control unit 50 can determine that the lawn mower 10 has come toa stop at time tb4 (F in FIG. 5). At this time point, the centralcontrol unit 50 may continue to activate both of the cylinders from thistime point tb4 onward so that the lower rotational speed Nb1 (which islower than Nb2) of the engine 100 may be regained in stable manner.

Once the lawn mower 10 has come to a stop, even though the blade clutch80 may be engaged, it can be assumed that the engine load is light.Therefore, the central control unit 50 lowers the rotational speed ofthe engine to Nb1 so that the fuel consumption may be minimized.

During the time interval between tb2 and tb3, only one of the cylindersis activated while the rotational speed of the engine is maintained atNb2 so that the fuel consumption may be minimized.

Preferably, when one of the cylinders is deactivated or during the timeinterval between time tb2 and time tb3, a highly lean mixture may besupplied to the combustion chamber of the active cylinder of the engineat a relatively wide throttle opening. In the illustrated embodiment,the throttle opening is increased from Thb2 to Thb4 at time tb2. Morespecifically, the central control unit 50 makes the fuel/air ratioleaner by adjusting the amount of fuel injection for the given airintake via the engine control unit 110 while the throttle opening isincreased from Thb2 to Thb4 at time tb2.

Thus, during the time interval between time tb2 and time tb3, the engine100 can be operated in a stable manner in spite of a highly lean mixtureowing to the light load, and the increasing of the throttle openingreduces the pumping loss of the engine. As a result, the engine can beoperated in a highly fuel efficient manner.

Furthermore, during the time interval between time tb2 and time tb3 orwhen one of the cylinders is deactivated, the ignition timing of theengine may be advanced and/or the duration of the spark of the sparkplug may be increased so that a highly stable combustion may bemaintained.

When the cylinder deactivation control is interrupted, and both of thecylinders are activated, the central control unit 50 changes the airfuel ratio from a lean value to a normal or stoichiometric value whileautomatically closing the throttle opening from Thb5 to Thb3. In otherwords, the central control unit 50 terminates the lean burn control attime tb3.

FIGS. 6 and 7 show a flowchart of the cylinder deactivation controlprocess including the starting of the forward travel of the lawn mower10. It should be noted that this is only exemplary, and does not limitthe scope of the present invention. After the blade switch is turned onby the operator, and the blade clutch 80 is engaged as a result, thecentral control unit 50 determines if the lawn mower 10 is movingforward or not according to the data or signal supplied by the detectionunit 40 which may include a wheel speed sensor (step ST21).

When the lawn mower 10 is traveling forward, the central control unit 50determines if a target rotational speed of the engine 100 is set at atarget rotational speed Nb2 for a grass cutting condition according to agrass cutting mode Ne set flag (step ST22). Initially or once the bladeclutch 80 is engaged, the grass cutting mode Ne set flag is set to “0”.

When the grass cutting mode Ne set flag is set to “0”, the centralcontrol unit 50 sets or raises the target rotational speed to Nb2 (stepST23). Initially or once the blade clutch 80 is engaged, the targetrotational speed is set to an idling target rotational speed Nb1 (anon-grass cutting condition). However, as the mass of the lawn mower issignificant particularly in the case of a ride-on mower, the targetrotational speed should be increased to the higher value of Nb2 in orderto avoid the stalling of the engine at the time of start off. Then, thecentral control unit 50 sets the grass cutting mode Ne set flag to “1”(step ST24), and the program flow returns to step ST21.

If the grass cutting mode Ne set flag is to “1” in step ST22, and therotational speed Ne of the engine 100 is therefore set to the prescribedrotational speed Nb2, the central control unit 50 determines if thecylinder deactivation control is to be initiated by referring to thecylinder deactivation flag indicating whether the cylinder deactivationcontrol is to be initiated or not (step ST25). The cylinder deactivationflag is initially set to “0”.

If the cylinder deactivation flag is “0” in step ST25, the centralcontrol unit 50 determines if the load on the engine 100 is high (stepST26). More specifically, the load on the engine 100 is determined to benot high when the throttle opening persists to be below the prescribedopening Thb3 for a prescribed time period.

If the load on the engine 100 is not high in step ST26, the centralcontrol unit 50 sets the cylinder deactivation flag to “1” (step ST27).On the other hand, if the load on the engine 100 is high in step ST26,the central control unit 50 sets the cylinder deactivation flag to “0”or maintains the cylinder deactivation flag at “0” (step ST28).

When the cylinder deactivation flag is set to “1” in step ST25, thecentral control unit 50 determines if the cylinder deactivation controlis to be terminated (step ST29). More specifically, the central controlunit 50 terminates the cylinder deactivation control if the throttleopening is greater than a value Thb5 which is higher than the prescribedopening value Thb3. Alternatively, the central control unit 50 mayterminate the cylinder deactivation control on the condition that thethrottle opening is greater than the high value Thb5, and therotationally speed of the engine does not stay stable at the prescribedrotational speed Nb2.

When the cylinder deactivation control is terminated in step ST29, thecentral control unit 50 sets the cylinder deactivation flag to “0” (stepST30). Otherwise, the program flow returns to step ST21. If thetraveling speed of the lawn mower is zero or if the lawn mower isstationary in step ST21, the central control unit 50 executes step ST31in a similar manner as in step ST25.

When the cylinder deactivation flag is “1” in step ST31, the centralcontrol unit 50 sets the cylinder deactivation flag to “0” (step ST32).Typically, when the traveling speed of the lawn mower 10 is zero, bothof the cylinders are activated as shown in B and F of FIG. 5. However,the lawn mower 10 may come to a stop (the traveling speed of the lawnmower may become zero) while one of the cylinders is deactivated. It mayalso be configured such that, under such a circumstance, the cylinderdeactivation flag may be set to “1” in step ST31.

When the cylinder deactivation control is not detected in step ST31 orwhen cylinder deactivation flag is set to “0” step ST32, the centralcontrol unit 50 sets the target rotational speed of the engine to theidling rotational speed Nb1 or maintains the idling rotational speed Nb1(step ST33). The central control unit 50 then sets the grass cuttingmode Ne set flag to “0” or maintains this flag at “0” (step ST34). Then,the program flow eventually returns to step ST21.

FIG. 8 is a time chart showing the mode of operation of the lawn mower10 including time periods where the lawn mower is traveling forward,stationary and traveling rearward. While the blade clutch 80 is engagedby the operator by turning on the blade switch provided on the operationconsole 60, the lawn mower 10 which has been traveling forward at speedVc3 is brought to a stop at time tc2. The detection unit 40 shown inFIG. 1 detects the traveling speed of the lawn mower 10, and then sendsa signal or data indicating the stationary condition of the lawn mower10 to the central control unit 50 at time tc2.

The fact that the lawn mower 10 is stationary typically indicates thatthe load on the engine 100 is light. However, it is also possible thatthe engine load is high because the blade clutch 80 is engaged, and thecutting blade 70 may be mowing grass. Therefore, the central controlunit 50 still keeps both of the cylinders activated at time tc2.

Then, the central control unit 50 evaluates the probability of theengine encountering a high load after time tc2. If the probability of alight engine load is high following time tc2, the central control unit50 deactivates one of the cylinders.

The probability of the engine load being light can be positivelyincreased according to the present invention. For instance, the heightof the cutting blade 70 can be automatically increased from a normalheight H2 to a highest possible height H3 at time tc2 by using theheight adjustment mechanism 90 for adjusting the height of the bladedeck. This is accomplished by setting a blade height control flag to“1”.

The higher the cutting blade 70 is, the smaller the cutting load of thecutting blade 70 becomes. When the blade deck 75 is placed in thehighest position, the cutting blade 70 typically does not cut grass atall. When the cutting blade 70 is higher than the expected height of thegrass, the cutting blade 70 consumes substantially no power of theengine or, in other words, the probability of a light engine load ishigh.

Thus, the central control unit 50 initiates the cylinder deactivationcontrol at time tc3, and deactivates one of the cylinders. In otherwords, when the blade clutch 80 is engaged, and both of the cylindersare activated, the central control unit 50 determines that the cylinderdeactivation control should be initiated, optionally, after raising theheight of the cutting blade to the highest possible position H3.

More specifically, the central control unit 50 determines at time tc2 ifthe lawn mower 10 continues to travel forward or has come to a stop. Ifthe lawn mower 10 has come to a stop, the central control unit 50automatically raises the cutting blade 70 from height H2 to height H3during the time period of from tc2 to tc3, and initiates the cylinderdeactivation control at time tc3 (A, D and E in FIG. 8).

Then, suppose that the operator operates a transmission lever(forward/reverse switch) on the operation console 60 to command thecentral control unit 50 to put the gear in the reverse. The centralcontrol unit 50 detects the selection made by the transmission lever attime tc4 (F in FIG. 8).

As a result, the lawn mower 10 starts traveling rearward, and a signalor data indicating the rearward movement is forwarded from the detectionunit 40 to the central control unit 50 (D in FIG. 8). During the timeinterval between tc2 and tc6 where the lawn mower 10 is not travelingforward, or, in other words, where the lawn mower 10 is stationary ortraveling rearward, the central control unit 50 maintains the cuttingblade 70 at height H3 (E in FIG. 8).

The operator then decides to drive the lawn mower 10 forward at timetc6, and the central control unit 50 receives a signal or dataindicating a forward speed greater than zero from the detection unit 40at time tc6 (D in FIG. 8). At this point or time tc6, the centralcontrol unit 50 terminates the cylinder deactivation control, andactivates both of the cylinders (A in FIG. 8). At the same time, thecentral control unit 50 sets the blade height control flag to “0” sothat the height of the cutting blade 70 is lowered from H3 to H2 (E inFIG. 8).

The central control unit 50 sets the blade height control flag to “0” attime tc6, and automatically lowers the height of the blade 70 from H3 toH2 (E in FIG. 8). The central control unit 50 then determines that thelawn mower 10 is steered to the right at time tc7 with a steering angleexceeding a prescribed threshold value S2 (F in FIG. 8). The centralcontrol unit 50 detects the right turn of the lawn mower 10 via asteering angle sensor included in the detection unit 40.

When a large steering angle is detected, it is highly likely that thelawn mower 10 is being relocated from one location to another or makinga U turn at a perimeter of the lawn so that the probability of theengine load being light is high. Therefore, when a large steering angle(exceeding S2) is detected, the central control unit 50 raises theheight of the cutting blade 70 from H2 to H3 at time tc7, and, upon thecutting blade 70 reaching the height H3 at time tc8, initiates thecylinder deactivation control at time tc8 (A, E and F in FIG. 8).

Also, upon detecting that the steering angle has exceeded the thresholdvalue S2 at tc7, not only the height of the cutting blade 70 is raisedto H3 but also the traveling speed of the lawn mower 10 is automaticallyreduced from Vc3 to Vc2 (D in FIG. 8) by setting a steering speedreduction flag to “1” at time tc7. By thus automatically reducing thetraveling speed of the lawn mower 10, the precision of the turningmaneuver of the lawn mower 10 can be improved, and/or the turning radiusof the lawn mower 10 can be minimized.

In the illustrated embodiment in which a throttle by wire system isincorporated in the engine 100, when the steering speed reduction flagis set to “1”, the central control unit 50 causes the traveling speed ofthe lawn mower 10 to be automatically reduced from Vc3 to Vc2 via theengine control unit 110. Alternatively or additionally, the centralcontrol unit 50 may apply a brake to the lawn mower 10 to achieve therequired speed reduction.

If the lawn mower 10 consists of a hybrid lawn mower 10 which uses anelectric motor as a power source for powering the propelling device ofthe lawn mower and an internal combustion engine for driving the cuttingblade 70, the central control unit 50 can reduce the traveling speed ofthe lawn mower by suitably controlling the electric power supplied tothe electric motor.

Once the cutting blade 70 has been raised to the height of H3 at timetc8, the central control unit 50 initiates the cylinder deactivationcontrol (A and E in FIG. 8). When the steering angle is reduced to zeroat tc9, and the lawn mower 10 has thereby started traveling forward, thecentral control unit 50 terminates the cylinder deactivation control,and activates both of the cylinders (A and F in FIG. 8). This isadvantageous because, typically, once the lawn mower 10 has startedtraveling straight forward, the cutting blade 70 is required to cutgrass, and it is therefore highly likely that the engine load willincrease.

FIGS. 9 and 10 show a flowchart illustrating the mode of operation ofthe lawn mower 10 during a time interval in which the travelingdirection of the lawn mower 10 is reversed, and the lawn mower 10 issteered by a relatively large angle. Suppose that the blade clutch 80 isinitially engaged. The central control unit 50 determines if the lawnmower 10 is steered by detecting a steering angle exceeding theprescribed threshold value S2 according to a signal or data obtainedfrom the detection unit 40 (step ST41).

More specifically, when the absolute value of the steering angle issmaller than the threshold value S2, the central control unit 50determines if the transmission system of the lawn mower 10 is placed inthe state for the forward movement according to the data or signal fromthe FWD/RVS switch in the operation console 60 (step ST42).

Upon detecting the state for the forward movement of the lawn mower 10,the central control unit 50 determines if the lawn mower 10 is beingaccelerated according to the data or signal from the detection unit 40which may include an accelerator pedal sensor (step ST43). Morespecifically, the central control unit 50 determines that the lawn mower10 is not accelerating when the depression stroke of the acceleratorpedal is zero, and that the lawn mower 10 is accelerating when thedepression stroke of the accelerator pedal is not zero.

Upon detecting that the lawn mower 10 is not accelerating, the centralcontrol unit 50 determines if the lawn mower 10 is traveling forwardfrom the data or signal from the detection unit 40 which may include awheel speed sensor (step ST44). More specifically, the central controlunit 50 determines that the lawn mower 10 is not traveling forward whenthe wheel speed is zero, and that the lawn mower 10 is traveling forwardwhen the wheel speed is not zero.

When the traveling speed of the lawn mower is zero, the central controlunit 50 sets the blade height control flag to “1” (step ST45). In theinitial condition or when the blade clutch 80 is engaged, the bladeheight control flag is set to “0”.

If the lawn mower 10 is accelerating in step ST43, the blade heightcontrol flag is set to or maintained at “0” (step ST46). Similarly, ifthe traveling speed of the lawn mower 10 is not zero in step ST44, theblade height control flag is set to or maintained at “0” (step ST46).

If the transmission system of the lawn mower 10 is not in the state forforward travel in step ST42, the blade height control flag is set to “1”(step ST47). Similarly, if the absolute value of the steering angle isgreater than the prescribed threshold value S2, the blade height controlflag is set to “1” (step ST48).

Then, the central control unit 50 may set the steering decelerationcommand flag to “1” (step ST49). Initially or when the blade clutch 80is engaged, the steering deceleration command flag is set to “0”. Whenthe deceleration during the cornering maneuver is completed, the centralcontrol unit 50 sets the steering deceleration command flag back to “0”.

The central control unit 50 determines if the blade height control flagis “1” in step ST50. If the blade height control flag is “1”, thecentral control unit 50 sets the height of the blade 70 to the highestposition H3 or the eighth stage (step ST51). More specifically, thecentral control unit 50 keeps moving the blade deck 75 upward whilemonitoring the data or signal from the height adjustment mechanism 90until the highest position H3 (eighth stage) is reached (step ST52).Once the blade 70 has reached the highest position, the blade heightcontrol flag is set to “0 ”.

At the same time, the central control unit 50 sets the cylinderdeactivation flag to “1” (step ST53). In the initial condition or whenthe blade clutch 80 is engaged, the cylinder deactivation flag is set to“0”.

If the blade height has not reached the highest position or the signalreceived from the height adjustment mechanism 90 indicates that theblade height is lower than the highest position H3 (in the seventh stageor lower) in step ST51, the central control unit 50 moves the blade deck75 upward by one stage (step ST54).

If the blade height control flag is not “1” in step ST50, the centralcontrol unit 50 determines if the height of the blade 70 should be setto a desired height (such as the fourth stage) according to the settingentered from the operation console 60 by the operator (step ST55).

For instance, when the current blade height is in the highest position(the eighth stage), and the desired height is a certain number of stageslower than the highest stage (fourth stage, for instance), or in otherwords, the current blade height is higher than the desired heightaccording to the signal from the height adjustment mechanism 90 for theblade deck 75, the central control unit 50 lowers the height of theblade 70 by one stage (step ST56). At the same time, the central controlunit 50 sets the cylinder deactivation flag to “0” (step ST57).

If the signal received from the height adjustment mechanism 90 indicatesthat the blade 70 has reached the desired height in step ST55, thecentral control unit 50 stops the downward movement of the blade 70(step ST58). At the same time, the central control unit 50 sets thecylinder deactivation flag to “0” (step ST59). In each of the cases, theprogram flow eventually returns to step ST41.

Although the present invention has been described in terms of preferredembodiments thereof, it is obvious to a person skilled in the art thatvarious alterations and modifications are possible without departingfrom the scope of the present invention which is set forth in theappended claims. The contents of the original Japanese patentapplication on which the Paris Convention priority claim is made for thepresent application as well as the contents of the prior art referencesmentioned in this application are incorporated in this application byreference.

1. A lawn mower, comprising: a lawn mower main body provided with apropelling device; a power source for selectively powering thepropelling device; a traveling state sensor for detecting a travelingstate of the lawn mower; an internal combustion engine having aplurality of cylinders and supported by the lawn mower main body; anengine control unit for selectively deactivating at least one of thecylinders; a cutting blade rotatably supported by the lawn mower mainbody via a cutter deck and connected to the engine in a powertransmitting relationship; a blade clutch provided in a powertransmission path between the engine and the cutting blade; a heightadjustment mechanism provided on the cutter deck for adjusting a heightof the cutting blade; and a central control unit for controlling anoperation of the blade clutch, the height adjustment mechanism and theengine control unit; wherein the central control unit is configured tocause the engine control unit to deactivate at least one of thecylinders when a prescribed operating condition is met, and to raise thecutting blade to a prescribed elevated height before deactivating the atleast one of the cylinders.
 2. The lawn mower according to claim 1,wherein the central control unit is configured to deactivate at leastone of the cylinders when the lawn mower is not traveling forward. 3.The lawn mower according to claim 1, wherein the central control unit isconfigured to maintain the cutting blade at the prescribed elevatedheight when the lawn mower is commanded to travel rearward or istraveling rearward.
 4. The lawn mower according to claim 1, wherein thelawn mower further comprises a steering angle sensor, and the centralcontrol unit is configured to deactivate at least one of the cylinderswhen the lawn mower is traveling forward, and a steering angle greaterthan a prescribed value is detected.
 5. The lawn mower according toclaim 4, wherein, when the lawn mower is traveling forward, and asteering angle greater than the prescribed value is detected, thecentral control unit further raises the cutting blade to a prescribedelevated height and decelerates the lawn mower.
 6. The lawn moweraccording to claim 1, wherein the prescribed elevated height correspondsto a highest possible position of the cutter deck.